Taking an Accurate Look at SSD Write Endurance

Last year, I posted a rebuttal to a paper describing the future of flash memory as ‘bleak’. The paper went through great (and convoluted) lengths to paint a tragic picture of flash memory endurance moving forward. Yesterday a newer paper hit Slashdot – this one doing just the opposite, and going as far as to assume production flash memory handling up to 1 Million erase cycles. You’d think that since I’m constantly pushing flash memory as a viable, reliable, and super-fast successor to Hard Disks (aka 'Spinning Rust'), that I’d just sit back on this one and let it fly. After all, it helps make my argument! Well, I can’t, because if there are errors published on a topic so important to me, it’s in the interest of journalistic integrity that I must now post an equal and opposite rebuttal to this one – even if it works against my case.

First I’m going to invite you to read through the paper in question. After doing so, I’m now going to pick it apart. Unfortunately I’m crunched for time today, so I’m going to reduce my dissertation into the form of some simple bulleted points:

The flash *page* size (8KB) and block sizes (2MB) chosen more closely resemble that of MLC parts (not SLC – see below for why this is important).

The paper makes no reference to Write Amplification.

Perhaps the most glaring and significant is that all of the formulas, while correct, fail to consider the most important factor when dealing with flash memory writes – Write Amplification.

Before geting into it, I'll reference the excellent graphic that Anand put in his SSD Relapse piece:

SSD controllers combine smaller writes into larger ones in an attempt to speed up the effective write speed. This falls flat once all flash blocks have been written to at least once. From that point forward, the SSD must play musical chairs with the data on each and every small write. In a bad case, a single 4KB write turns into a 2MB write. For that example, Write Amplification would be a factor of 500, meaning the flash memory is cycled at 500x the rate calculated in the paper. Sure that’s an extreme example, but the point is that without referencing amplification at all, it is assumed to be a factor of 1, which would only be the case if you were only writing 2MB blocks of data to the SSD. This is almost never the case, regardless of Operating System.

After posters on Slashdot called out the author on his assumptions of rated P/E cycles, he went back and added two links to justify his figures. The problem is that the first links to a 2005 data sheet for 90nm SLC flash. Samsung’s 90nm flash was 1Gb per die (128MB). The packages were available with up to 4 dies each, and scaling up to a typical 16-chip SSD, that only gives you an 8GB SSD. Not very practical. That’s not to say 100k is an inaccurate figure for SLC endurance. It’s just a really bad reference to use is all. Here's a better one from the Flash Memory Summit a couple of years back:

The second link was a 2008 PR blast from Micron, based on their proposed pushing of the 34nm process to its limits. “One Million Write Cycles” was nothing more than a tag line for an achievement accomplished in a lab under ideal conditions. That figure was never reached in anything you could actually buy in a SATA SSD. A better reference would be from that same presentation at the Summit:

This shows larger process nodes hitting even beyond 1 million cycles (given sufficient additional error bits used for error correction), but remember it has to be something that is available and in a usable capacity to be practical for real world use, and that’s just not the case for the flash in the above chart.

At the end of the day, manufacturers must balance cost, capacity, and longevity. This forces a push towards smaller processes (for more capacity per cost), with the limit being how much endurance they are willing to give up in the process. In the end they choose based on what the customer needs. Enterprise use leans towards SLC or eMLC, as they are willing to spend more for the gain in endurance. Typical PC users get standard MLC and now even TLC, which are *good enough* for that application. It's worth noting that most SSD failures are not due to burning out all of the available flash P/E cycles. The vast majority are due to infant mortality failures of the controller or even due to buggy firmware. I've never written enough to any single consumer SSD (in normal operation) to wear out all of the flash. The closest I've come to a flash-related failure was when I had an ioDrive fail during testing by excessive heat causing a solder pad to lift on one of the flash chips.

All of this said, I’d love to see a revisit to the author’s well-structured paper – only based on the corrected assumptions I’ve outlined above. *That* is the type of paper I would reference when attempting to make *accurate* arguments for SSD endurance.

Introduction, Specifications and Packaging

Introduction

With newer and faster SSDs coming to market, we should not forget those capable controllers of yesteryear. There are plenty of folks out there cranking out products based on controllers that were until very recently the king of the hill. Competition is great for the market, and newer product launches have driven down the cost of the older SandForce 2281 SATA 6Gb/sec controller. ADATA makes a product based on this controller, and it's high time we gave it a look:

The ADATA XPG SX900 launched mid last year, and was ADATA's first crack at the eXtended capacity variant of the SandForce firmware. This traded off some of the spare area in the interest of more capacity for the consumer.

Introduction, Specifications and Packaging

Introduction

It has been just under a year since Intel released their 520 Series SSD, which was their second 6 Gb/sec SATA unit. Sporting a SandForce controller, that release helped bridge a high speed storage gap in their product lineup. One year prior, Intel dabbled in the mSATA form factor, releasing a 310 Series model under that moniker. The 310 showed up here and there, but never really caught on as the physical interface was admittedly before its time. While in hindsight it was a very good way to go towards establishing a fixed standard, the industry had already begun fragmenting on these smaller interfaces. The MacBook Air had already launched with a longer 'GumStick' shaped SSD, and Ultrabook makers were following suit with units that were physically identical yet not pin-compatible with that used in the Apple product.

Introduction, Specifications and Packaging

Introduction

OCZ has been in the SSD game for quite some time, and has previously done quite well mixing and matching hardware from other vendors into solutions of their own. It was a good way to put out a large array of products, fitting many a niche for a decent cost. Further, OCZ has always been known as somewhat of an underdog who tailored their parts more towards the power user / tweaker crowd. All of that said, they have been taking steps to become more of a major player in the SSD market, and the fruits of that labor begin their payoff today, with the release of the OCZ Vector:

A new Indilinx Controller?

The Vector comes equipped with a bunch of firsts for OCZ. The controller is OCZ's first 100% in-house part, and has been engineered from the ground up to be as high of a performing part as possible. There has been a paradigm shift within OCZ lately, and the Vector went through a large beta test phase *before* release, as to avoid the need for a series of rapid fire firmware updates just after the product ships. Vector should perform at or near its maximum potential today, not after some firmware updates seen months from now. Here's a look at the controller functional block diagram:

Introduction, Specifications and Packaging

Introduction

It's been a short while since we've seen a consumer SSD release from Intel, and with pressure coming from Samsung in the form of lower cost/GB 20nm flash, it was high time Intel followed suit. The Intel 335 Series launches today, and is essentially the same SandForce-driven product as their SSD 520 Series released earlier this year. The key change is this time around that controller will be driving Intel 20nm flash. This should bring a much needed price reduction to the SSD arena, as the 335 is not being marketed as a 'Pro' unit (like the Samsung's 840 Pro). So long as this new model performs similarly to the 520 Series, we should be in for a good, low cost SSD just in time for the Christmass shopping season.

Wireless storage for PC, Mac, iOS and Android

The premise is quite simple: take a portable hard drive with USB 3.0 support and add in the ability to share the unit wirelessly with up to 8 different machines and power it by a lithium-ion battery. Not only does the Gauntlet show up in your network as a mountable drive in Windows and Mac OS, the Gauntlet supports using free applications for iOS devices and Android devices to share and stream media.

There are some limitations that you might want to consider including the inability to access network-based devices when using the pass through Internet capability the Gauntlet provides. Also, data transfer performance on the wireless connectivity that the Gauntlet provides seemed pretty low, even with the 802.11n support.

Potential uses cases for the Gauntlet include any time you need a shared data source like working on group projects for school or the office, on-the-go storage for devices like Ultrabooks with smaller hard drives and users that have large media collections they want to use with smart phones and tablets.

Check out our full video review below!

Note that in the video, our early sample of the Gauntlet 320 has the "node" label on it; the Gauntlet Node is a separate device that is only a DIY enclosure WITHOUT an included hard drive. Originally there was a sticker cover the "node" label but incorrectly removed it before filming. Just a heads up!

Introduction and Internals

Introduction:

The Western Digital RAID Edition line of hard drives has been around for some time now, and has largely impressed us with each subsequent release. Since the launches of the RE4-GP and later, the faster spinning RE4, WD's enterprise line had been capped at the 2TB mark. Now that has changed with the introduction of a new line: simply named the RE Series:

Yup, that's right. 4 TeraBytes! With the Green and Red series capped at 3TB, this new RE is the largest capacity drive available from Western Digital. The catch is that, since it's tailored and built for enterprise use, it comes at a rather hefty price premium.

Introduction, Specifications and Packaging

Introduction

Last week, Samsung flew myself and a few of my fellow peers in the storage review community out to Seoul, Korea. The event was the 2012 Samsung SSD Global Summit:

At this event, Samsung officially announced their new 840 Pro, which we were able to obtain early under NDA and therefore publish in concert with the announcement. The 840 Pro was largely an incremental inprovement over their 830 Series. Newer, faster flash coupled with a higher clocked controller did well to improve on an already excellent product.

As the event closed, we were presented with the second model of the lineup - the 840. This model, sans the 'Pro' moniker, is meant more for general consumer usage. The first mass marketed SSD to use Triple Level Cell (TLC) flash, it sacrifices some write speed and long-term reliability in favor of what should become considerably lower cost/GB as production ramps up to full capacity. TLC flash is the next step beyond MLC, which is in turn a step after SLC. Here's a graphic to demonstrate:

Introduction, Specifications and Packaging

Introduction

Samsung has been at this SSD thing for quite some time now. The first SSD I bought was in fact a Samsung unit meant for an ultraportable laptop. Getting it into my desktop was a hack and a half, involving a ZIF to IDE adapter, which then passed through yet another adapter to convert to SATA. The drive was wicked fast at the time, and while it handily slaughtered my RAID-0 pair of 74GB VelociRaptors in random reads, any writes caused serious stuttering of the drive, and therefore the entire OS. I was clearly using the drive outside of its intended use, but hey, I was an early adopter.

Several SSDs later came the Intel X25-M. It was a great drive, but in its earliest form was not without fault. Luckily, these kinks were worked out industry-wide, and everyone quickly accelerated their firmware optimizations as to better handle random writes. Samsung took a few generations to get this under control. The first to truly get over this hump was the 830 Series, which launched earlier this year. It utilized a triple core Arm 9 CPU which was able to effectively brute force heavy random write workloads. It also significantly increased the speed and nimbleness of the 830 across the board, which combined with Samsung's excellent reliability record, quickly made it my most recommended series as of late.

...and now we have the 840 Series, which launched today. Well, technically it launched yesterday if you're reading from the USA. Here in Korea the launch started at 10 AM and spanned a day of product press briefings leading to the product NDA expiration at 8 PM Korea time. This review will focus on the 512GB capacity of the 840 Pro model. We will follow on with the 840 (non-pro) at a later date:

Introduction and Internals

Introduction:

I'm going to let the cat out of the bag right here and now. Everyone's home RAID is likely an accident waiting to happen. If you're using regular consumer drives in a large array, there are some very simple (and likely) scenarios that can cause it to completely fail. I'm guilty of operating under this same false hope - I have an 8-drive array of 3TB WD Caviar Greens in a RAID-5. For those uninitiated, RAID-5 is where one drive worth of capacity is volunteered for use as parity data, which is distributed amongst all drives in the array. This trick allows for no data loss in the case where a single drive fails. The RAID controller can simply figure out the missing data by running the extra parity through the same formula that created it. This is called redundancy, but I propose that it's not.

An overview of Thunderbolt Technology

The promise of Thunderbolt connectivity has been around for a couple of years now. Today, Thunderbolt is finally finding its way to the PC platform in the form of motherboards from ASUS and MSI. First unveiled as "Light Peak" at the Intel Developer Forum in 2009, the technology started out as a way to connect multiple devices to a system over a fiber optic cable (hence the 'light' in the name), though the final products have changed the implementation slightly.

The first prototype implementations actually used a USB-style connection and interface. It further required fiber optic cables. When it was renamed to Thunderbolt and then released in conjunction with a new lineup of Apple MacBook laptops, not only did the physical interface move to a mini-DisplayPort connection but the cable was made to use copper rather than fiber. Without diving too far into the reasons and benefits of either direction, the fact is that the copper cables allow for modest power transfer and are much cheaper than fiber optic variants would be.

Thunderbolt's base technology remains the same, however. It is a transfer standard that allows for 10 Gbps of bandwidth for each channel (bi-directional) and concurrently supports both data and display connections. The actual interface for the data path is based on PCI Express and connected devices actually appear to Windows as if they are internally connected to the system which can offer some interesting benefits – and headaches – for hardware developers. The display connection uses the DisplayPort standard and can be used along with the data connection without affecting bandwidth levels or performance.

For current Intel processor implementations, the Thunderbolt connection is supported by a separate controller chip on the motherboard (or a riser card) – and some routing is required for correct usage. The Thunderbolt controller does not actually include a graphics controller, so it must be fed an output from another graphics processor, obviously in this case directly from the Ivy Bridge / Sandy Bridge processors. In theory, these could be from other controllers, but with the ubiquitous nature of integrated processor graphics on IVB and SNB processors, this is going to be the implementation going forward according to motherboard and system designers.

ioSafe: Introduction and Internals

Introduction:

Cloud storage is all the talk these days, and our own Tim Verry has been hard at work detailing as much of it as he can keep up with. While all of us at PCPer currently use cloud based solutions for many of the day-to-day goings on, it's not for everyone, and it tends to not be for very large chunks of data, either. Sometimes local storage is just the way to go – especially when you want to be the one in absolute control of the reliability and integrity of your data.

The general rule for proper backups is to have your local copy, a local backup (RAID is *not* a backup), and an additional off-site backup to cover things like theft, fires or floods. So lets say you simply have too much sensitive data for your internet connection to support bulk transferring to an off-side / cloud storage location. Perhaps the cloud storage for that much space is simply cost prohibitive, or your data is sensitive enough that – despite encryption – you don't want it leaving your network and/or premesis? Perhaps you're just stubborn and want only one backup of your data? I think I might have the answer you've been looking for – behold the ioSafe SoloPRO:

What is this thing, you may ask? On the inside it's one of the available 1, 2, 3, or even 4TB 3.5" hard drives. On the outside it's a very durable and solid steel enclosure. The hard drive is wrapped in a thermally conductive yet water resistant 'HydroSafe' foil that enables water resistance rated at a 10 ft depth for 3 days with no data loss. The bonus, however, is not the water resistance - that featuer is present primarily to battle the side effects of something much more drastic - the ioSafe is fire-proof. That feature comes from what sits between the steel casing and the shrink wrapped hard drive - something ioSafe calls a DataCast (pictured below):

Internals:

I'm going to break from my normal warranty voiding and show a photo from this past Storage Visions conference at the Consumer Electonics Show, where an ioSafe was already cracked open for our viewing pleasure:

Inside and Out

When you are a little fish in the great big pond of PC builders, you need to do something to stand out from the rest. The people behind DV Nation apparently were well aware of that when entering the system vendor business and offering up SSDs to every single system configuration. Through a new system they are offering, provocatively named the "RAMRod PC", DV Nation provides a pre-built system that has some very unique components and configuration settings.

Built around the Antec Three Hundred Two chassis, the first glance at the RAMRod doesn't really indicate anything special is going on under the hood. But let's take a quick look at the specs:

Intel Core i7-3820 @ 4.4 GHz

64GB DDR3-1600 Memory from G.Skill

Radeon HD 6990 4GB

2x Seagate Momentus XT 750GB Hybrid HDD in RAID-0

OCZ RevoDrive 3 X2 480GB PCIE SSD

RAMCache: SuperSpeed Supercache 8GB on PCIE SSD, 8GB on Momentus

RAMDisk: 42GB ROMEX Primo rated at 8000 MB/s

Cost: $5,400

Obviously there is a LOT of storage work going on in the RAMRod and the purpose of the rig is to be the fastest pre-configured storage available anywhere. If you are looking for a cheaper version of this system you can get a base model with 16GB of memory, 10GB RAMDisk, 2GB RAMCache, 240GB PCIe SSD, single standard hard drive and even at GTX 680 for $2999.

Let's take a quick walk around the rest of the system before diving into the benchmarks!

Background and Internals

A little over two weeks back, Intel briefed me on their new SSD 910 Series PCIe SSD. Since that day I've been patiently awaiting its arrival, which happened just a few short hours ago. I've burned the midnight oil for the sake of getting some greater details out there. Before we get into the goods, here's a quick recap of the specs for the 800 (or 400) GB model:

"Performance Mode" is a feature that can be enabled through the Intel Data Center Tool Software. This feature is only possible on the 800GB model, but not for the reason you might think. The 400GB model is *always* in Performance Mode, since it can go full speed without drawing greater than the standard PCIe 25W power specification. The 800GB model has twice the components to drive yet it stays below the 25W limit so long as it is in its Default Mode. Switching the 800GB model to Performance Mode increases that draw to 38W (the initial press briefing stated 28W, which appears to have been a typo). Note that this increased draw is only seen during writes.

Introduction

It's been a long while since we've looked at a hard drive, and how fitting that it be a new model of the Western Digital VelociRaptor! Western Digital appears to be on a somewhat fixed 2-year cycle with these, as out 600GB VelociRaptor Review went up two Aprils ago, and the 300GB two years prior to that. Well then, let's take a look at this new model!

(from left) 300GB, 600GB, and finally the 1TB VelociRaptor

Here's the old school VelociRaptor logo (from back when they were less than 100GB!)

Introduction, Specifications, and Packaging

Introduction

OCZ has been in the SSD game for quite some time now. Their first contender was the OCZ Vertex, which we reviewed back in Febuary of 2009. While the original Vertex was powered by an Indilinx BareFoot controller, the Vertex line switched over to SandForce for the second and third generations. The fourth generation brings Indilinx back to the Vertex, this time with the Everest 2. You may recall Everest made its first appearance in the OCZ Octane, which has already proven itself to be a solid contender in the market.

Before we get into the meat and portatoes, we'll kick this off by saying this will not be a typical Vertex 4 review. We had benches run on 512GB and 256GB Vertex 4 samples, but the numbers we were seeing seemed 'off', so OCZ provided me with an alpha/engineering level firmware late last night. I suspect most other reviews you read today will include results from the 1.30 initial shipping firmware, or perhaps from the 1.31 bugfix firmware (which corrected an issue with secure erasure), but this piece will cover both 1.30 and a newer 1.52 interim build. Sometimes it's necessary to burn the midnight oil in the interest of presenting the full picture (or one as complete as possible) to our readers, and this was one of those pieces. We will revisit the Vertex 4 again very soon in the form of a more final product review, but for now we'll go with what we've got.

Introduction, Specifications, and Packaging

Introduction

Samsung has been in the SSD business for a good long while now. My first "serious" SSD setup consisted of a pair of 32GB G.Skill 'FlashSSD's in a RAID. A few months later I upgraded to an Intel X25-M, starting working for PCPer, and have since seen a slew of different controller types come and go. Of those, Samsung and Intel both come to mind as the most reliable controllers out there. Of those two, Samsung has always been the primary choice of PC OEMs. It may have been because the Samsung controllers have always leaned towards the slow-but-steady approach. Other fire breathing controllers would be quick out of the gate but slow over time as fragmentation effects set in, while Samsung controllers would take the hit on random IOPS, but they maintained that lower level even after repeated and sustained abuse. They were not the fastest, but as a testament to their consistency, I continue to use one of the two aforementioned G.Skill drives in the PCPer Storage Testbed to this day.

Overcoming Hurdles

A paper, titled “The Bleak Future of NAND Flash Memory” was recently jointly published by the University of California and Microsoft Research. It has been picked up by many media outlets who all seem to be beating the samemorbiddrum, spinning tales of a seemingly apocalyptic end to the reign of flash-based storage devices. While I agree with some of what these authors have to say, I have reservations about the methods upon which the paper is based.

TLC and beyond?

The paper kicks off by declaring steep increases in latency and drops in lifetime associated with increases in bits-per-cell. While this is true, flash memory manufacturers are not making large pushes to increase bits-per-cell beyond the standard MLC (2 bits per cell) tech. Sure some have dabbled in 3-bit MLC, also called Triple Level Cell (TLC) which is a bit of a misnomer since storing three bits in a cell actually requires eight voltage level bands, not three as the name implies. Moving from SLC to MLC doubles density, but the diminishing returns increase sharply after that – MLC to TLC only increases capacity by a another 1.5x, but sees a 2-4x reduction in performance and endurance. In light of this, there is little demand for TLC flash, and where there is, it’s clear by the usage cases that it is not meant for anything beyond light usage. There's nothing wrong with the paper going down this road, but the reality is that increasing bits per cell is not the envelope being pushed by the flash memory industry.

Wait a second – where is 25nm MLC?

Looking at the above we see a glaring omission – 25nm MLC flash, which has been around for close to two years now, and constitutes the majority of shipping flash memory parts currently in production. SLC was also omitted, but I can see the reason for this – it’s hard to get your hands on 25nm SLC these days. Why? Because MLC technology has been improved upon to the point where ‘enterprise MLC’ (eMLC) is rapidly replacing SLC even despite the supposed reduction in reliability and endurance over SLC. The reasons for this are simple, and are completely sidestepped or otherwise overlooked by the paper:

Introduction, Specifications, and Packaging

Introduction

Today we take a look at Intel's newest 6Gb/sec SATA SSD - the 520 Series. This is the second non-Intel controller to appear in one of their products. The first was the Marvell controller, which appeared in the 510 Series last March. This time around, Intel has gone with SandForce. This should leave at least one SATA 6Gb/sec model to be released. Taylorsville is the code name for the next SATA 6Gb/sec native-Intel controller, which has been on their roadmap since mid-2010 but has yet to actually materialize. While Taylorsville development continues, Intel has stop-gapped the 6Gb/sec slot with the 510 and now the 520 Series. Intel seemingly worked wonders with the stock Marvell firmware, and while the Marvell controller was much improved over stock, it still lagged far behind other higher performing SATA 6Gb/sec solutions. The SandForce was one of the much more capable controllers eating the 510's lunch, but how much further could Intel improve upon the SandForce firmware?

I guess a good question to answer up front is - What took them so long?!?! The answer is a bit complicated. Intel has actually been working on getting the 520 out the door for over a year now. They had to start with the same base SandForce firmware but accomplish two things for their version to be successful:

They didn't say so directly, but I can only imagine Intel's process was plagued by multiple 'back to the drawing board' moments. Trying to one-up competition like OCZ can't be easy as they've been tweaking SandForce firmware since the very beginning. There's also those nasty bugs that would cause random BSOD's or even permanently brick the drive. Such failures have no place in an Intel SSD. Intel's upper limit for each SSD line is a 0.75% annual failure rate, and we've seen SandForce SSD's failing at a higher rate than that this past year.

With each tweak made, Intel would have to once again pass their drives through another round of full validation testing. This is no small task for Intel. As an example: It took Intel just a couple of weeks to recreate and correct the long-term performance issue I discovered back in 2009, but despitemountingpressure, they could not release the updated firmware until it had successfully passed their validation a full three months later. Intel takes this testing very seriously, and that's what leads people to trust their reliability.

Introduction, Specifications, and Packaging

Introduction

A couple of days ago we looked at a pair of SSD's from Patriot. Next up is a pair of SSD's from Corsair. These are another two SandForce controlled units, but this time it's Async IMFT flash vs. Sync IMFT flash:

We'll carry the Patriot Pyro (IMFT Async) into the results for comparison, and keeping the other benchmark OCZ and Intel models in with the mix of results. The OCZ Vertex 3 and Agility 3 will again share the same SandForce controller, but OCZ has been known to add many performance tweaks to their firmware. Let's see if Corsair was able to use 'tweaked' firmware or instead went with the stock one provided by SandForce.

Specifications

The Corsair Force 3 and Force GT are both available in the following capacities:

60GB

90GB

120GB

180GB

240GB

480GB

The added capacity points are a bonus of how IMFT can stack their dies in 'odd' multiples (i.e. 3 per package, making a 24GB TSOP). Varying slightly from low to high capacities (and across the two models), specs range from 490 to 525 MB/sec writes and 550 to 555 MB/sec reads. 60GB models get 80,000 4K IOPS and the rest get a rating of 85,000 4K IOPS. Corsairs specs indicate IOMeter 2008 was used for this test, and it's important to note that 2008's writes were a repeating pattern that is easily and fully compressible by the SandForce controller, meaning those specs were derived using fully compressible data.